#7403R-EN

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How do birds fly? Since ancient times, humankind has wanted to fly through the sky. We envied the birds who fly so freely, and began to study the principles of flight through birds. Now we too can fly. Birds fly in more than one way. Finches must flap their wings nonstop and eagles glide through the sky. When observed through magnified slow motion birds not only flap their wings up and down but rely on arm motions similar to the butterfly swimming stroke; they extend outwards when striking downwards and retract inwards when striking upwards. (diagram 3)

(diagram 3)

The method that birds use to flap their wings allows them to feel the force of air and use it to carry their wings upwards; they push air behind them to accept a larger force. This force is known as lift.

The principles of lift Resistance is the force that pulls an object when it is moving forward; lift is the atmospheric force that lifts it vertically, but where does it come from? It is dependent on the density, speed, viscosity, and compression of air. Airflow passes through an object's surface and shape, and the angle between the object and airflow. Their relationship is highly complicated but was later defined by Bernoulli's law. (diagram 4)

Bernoulli's law

LIFT

(diagram 4)

The law was proposed by Daniel Bernoulli in 1738 in a paper titled <Hydrodynamica>. Simply put, the theory states that "when flow speed increases, pressure decreases". Bernoulli utilized Newton's study of kinematics and the theory of energy conservation (i.e. energy+potential energy=constant) to deduce his law: energy+pressure=constant. In other words, when an object's flow speed increases pressure will decrease because of the law of energy conservation. Airplanes depend on this theory to fly in the sky. "When an object's flow speed differs from those around them, the object with faster flow speed will have lower pressure causing pressure around the object to pressure the object with faster flow speed". If an object can move, it is usually affected by this type of force and moves towards the direction of force. The backs of planes are designed to be curved and their bottoms are designed to be flat to allow airflow on the back to travel faster and utilize the higher pressure on the bottom to support the plane's weight in the air.

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